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In 1935, to meet Air Ministry Specification F5/34, calling for a single-seat monoplane interceptor armed with six or eight machine-guns, a retractable undercarriage was required and an enclosed cockpit; a speed of at least 275mph (442kph) at 15,000ft (4,572m) was stipulated. This requirement was taken up by a number of firms. Bristol produced the Type 146 (835hp/622kW Bristol Perseus). Vickers brought their Jockey Mk II into approximate line with the requirements as the Venom (625hp/466kW Bristol Aquila). Henry Folland produced his last design for Gloster, the G.38 (840hp/626kW Bristol Mercury IX).

None of the aircraft built to this specification achieved production status but ultimately produced the Hurricane and the Spitfire.

The single-seat all-metal cantilever monoplane was powered by an 840hp Mercury IX nine-cylinder radial engine and carried an armament of eight 7.7mm Browning guns. This aircraft suffered a protracted development owing to the company's preoccupation with the Gladiator. The first of two prototypes did not commence flight trials until December 1937, with the second following in March 1938. By the time that the Gloster fighter made its debut, the Hurricane had entered service and the Spitfire had reached production, and further development of the Mercury-engined monoplane was not pursued.